GdwnsnHo
Banned
Don't forget that nationalism didn't exist in Roman times. Almost nobody felt as a "Celt", "German" or "Greek" - most of one's lifetime, you thought that you are citizen of Athens, or warrior of the Suebian tribe, or member of the Jewish chosen people; the Greeks only united after being attacked from outside, while the Italians fought three (?) wars to be united as a nation instead of living in peace as Austrian subjects.
Well that certainly isn't true. At least regarding feeling part of a group larger than your tribe.
The Gauls did see themselves all as Gauls, just no reason to unite as a single group until Julius Caesar and Vercengetorix. They were essentially the tribal equivalent of cousins. Vercengetorix is a nationalist hero even now in France, for inspiring their first attempt to unite and survive.
There are also distinctive tones of Greek Nationalism before Alexander-the-freaking-great. You had Boetia, Attica, and the Peloponesse all deriding Macedon for not being "Proper Greeks". They just didn't see their Greek-ness as a reason to unite. They didn't end up uniting because of the Persians (even if a letter was involved), but because one particularly powerful Macedonian smacked them all down and united them. Hell, they invented the term Barbarian to illustrate people who weren't able to speak properly!